1. Technical Field
The present invention relates to an active matrix flat panel display and, more particularly, to an organic light emitting diode capable of improving luminance per pixel unit by forming a cathode electrode which surrounds an organic luminescent layer, thereby focusing light per pixel unit.
2. Related Art
Generally, light efficiency of an organic light emitting diode (OLED) is largely divided into internal light efficiency and external light efficiency. The internal light efficiency out of the light efficiency depends on the photoelectric conversion efficiency of an organic luminescent layer, while the external light efficiency is characterized as light coupling efficiency and depends on the index of refraction of each layer making up the OLED. An OLED needs to improve the characteristics of a display device, including luminance, life cycle, etc. as it has a lower external light efficiency compared with a flat panel display, such as a cathode ray tube (CRT), a plasma display panel (PDP), or a field emission display (FED).
Certain problems exist in the currently used OLED. Most importantly, light emission is not satisfactory due to the escape of reflected light from the structure of the OLED. As a result, the overall luminance of the OLED is reduced, and this provides a less efficient device. Another problem with current OLED device is that its life is shortened due to the necessity to increase the driving voltage applied to it in order to compensate for the aforementioned reduced luminance.